Supercritical fluid extraction systems use carbon dioxide (CO2) at high pressure and high temperature, typically 10,000 psi and 150 C. These systems are environmentally benign and “green” since they generally do not rely on the use of sometimes toxic chemicals to extract a desired end product compounds from a starter matrix material. In its supercritical state, CO2 has both gas-like and liquid-like qualities, and it is this dual characteristic of supercritical fluids that provides the ideal conditions for extracting compounds with a high degree of recovery in a short period of time.
A major component of supercritical fluid systems is a pressure vessel which contains the CO2 and the matrix material including the desired end product compound which is being extracted. Under normal circumstances, the CO2 is contained in the vessel by shut off valves on either end of the vessel. One valve is an inlet valve and one valve is an outlet valve, both of which are both fluidly coupled to corresponding inlet and outlet fluid ports on the vessel. The inlet valve opens and CO2 enters the vessel. At a predetermined pressure, the inlet valve closes and traps the CO2 inside the vessel. After some period of time, the outlet valve opens and the CO2 and the extracted end product compound or component of the matrix rush out of the vessel. Then the outlet valve closes and the cycle is complete.
But there are occasions when this simple cycle may encounter a problem in evacuating the pressure vessel. There may be times that the extract has physical properties making it a gluey or sticky material like a polymer resin and this material coats the interior surfaces of the vessel. When an operator tries to open the outlet valve in such a case, the gluey extract material may block or plug the outlet port. The operator must then shuts down the equipment and tries to bleed the vessel pressure down through the inlet port by opening the inlet valve, but this port may also be similarly blocked by the gluey extract material. The operator now has a bottled vessel that may contain 10,000 psi CO2 with no ready and reliable way to evacuate it in order to gain access to the vessel interior to remove the gluey extract.
Accordingly, an improved means to depressurize such pressure vessels under the foregoing conditions is desired.